It is the most vulnerable stage of the mayfly emergence when the insect dangles its nymphal abdomen below the film, and its adult wing profile is above the surface. This is one of the most important hatches in May, June and July on our high lakes, and the Sprout Callibaetis is a great choice when fish are fussy.
Plan to fish larger patterns early in the season and smaller ones later on. Best conditions are on overcast days between 11 a.m. and 4 p.m. Fish an emerger until the adults are on the surface then switch to the dry. The best idea is to keep a dry rod rigged and ready when the fish switch to dries.
Tie this one with olive thread on a No. 12-16 Tiemco 2487 hook. For the shuck and tail, use gray Z-Lon fibers. Wrap the abdomen with olive Antron dubbing. For the thorax, use olive Antron. The wingpost is fashioned out of white foam with a natural grizzly hackle tied parachute style.
— Gary Lewis, for The Bulletin